The present invention relates generally to the art of welding power supplies. More specifically, it relates to engine driven welding power supplies having output control based on engine speed.
Engine/generator driven welding power supplies typically include an engine, a generator, a welding power source, often a wire feeder, and one or more controllers. The components may be sold as a group, a single unit or individually.
The engine has a throttle which may have a range of speed selections and often has a control mechanism to allow operation at full throttle and idle. The generator output is often controlled using field current, and the welding power supply is controlled in response to a user set point or reference. The controller may be relatively complex, and control the components in a unified manner, or it may be individual controllers for each component, with little or no joint control of components.
Many controllers that treat the components as individual components rather than as part of a system may be inadequate. For example, a typical engine control (used outside of the welding art) might not be capable of responding to the very rapid increase in power needed when an arc is struck or the set point changed. Similarly, a welding power supply controller designed for utility power line voltage use might not adequately respond when the engine is slow to provide the needed power.
A controller for field current designed for a welding power supply is described in U.S. Pat. No. 5,734,147, entitled Method And Apparatus For Electronically Controlling The Output Of A Generator Driven Welding Power Supply, filed Sep. 8, 1995, and assigned to the assignee of the present invention. U.S. Pat. No. 5,734,147, is hereby incorporated by reference.
One problem with engine/generator driven welding power supplies that are not properly controlled is that it may be difficult to start the arc, especially in stick or MIG welding. Generally, a xe2x80x9chotxe2x80x9d start or higher current/power start is desirable so the stick does not become welded to the workpiece. But before an arc is initiated or struck, an engine/generator driven welding power supply generator is idling. It cannot provide a hot or high current/power start because the horsepower (which is transformed into output power) available while idling is much less than the horsepower available at higher RPM.
Experienced welders have attempted to get a hot start by xe2x80x9cdouble strikingxe2x80x9d or touching the stick to the workpiece before welding. This causes current to increase, and the engine to speed up out of idle, before the arc is struck. However, this caused marking of the workpiece that was unacceptable for some x-ray quality welds or welds requiring a high surface quality. Also, this may not be a satisfactory solution for heavy loads or for CV applications.
Accordingly, U.S. Pat. No. 5,734,147 teaches to provide a hot start by giving an additional boost of current when the arc is struck. Unfortunately, this sometimes caused the engine to stall, because the called for output power was greater than the horsepower available (after accounting for system inefficiencies which may be about 50%) at lower RPM.
An engine/generator driven welding power supplie is likely to stall when more power is drawn than is capable of being provided. This is more likely to happen at lower RPM, because less horsepower is available at lower RPM than at higher RPM.
One attempted solution to that problem is to increase the engine speed at idle. This undesirably increases fuel consumption and reduces engine life. An alternative attempted solution is to increase the engine speed from idle to a higher speed. Another attempted solution is to temporarily reduce the output, until the likelihood of a stall is reduced. Both of these methods are suggested in application Ser. No. 08/858,129, filed May 19, 1997, entitled Engine Driven Invertor With Feedback Control, which is owned by the assignee of this invention and is hereby incorporated by reference.
However, the response of engine speed to throttle changes is often not fast enough to prevent stalling, particularly if the load (output power) had been quickly increased when the engine is at a low speed. Also, reducing output power can cause additional problemsxe2x80x94lower power can have an adverse impact on the arc. Thus, the competing interests of reducing power to avoid engine stalls while maintaining power to maintain a quality arc were necessarily properly balanced, particularly when the power reduction was merely on or off, and not variably controlled.
For example, the prior art does not teach to reduce the output by an amount responsive to operating conditions such as engine speed or output current, power, load, setpoint etc. In other words, it does not teach to have greater reduction in output power when the engine is slower, or the output is greaterxe2x80x94the reduction is the same regardless of the severity of the stall conditions and the conditions of the arc.
The Miller(trademark) BlueStar(trademark) welding power supply tried to account for different severity of stall conditions by increasing the xe2x80x9cthrottle backxe2x80x9d of output power as RPM decreased. This was done for all output currents even though at some output currents the load was not large enough to be likely to cause a stall. The reduction at lower currents often unduly reduced the quality of the arc. Thus, this system did not balance the need for power reduction to avoid a stall, and the need for power maintenance to help arc quality.
Accordingly, a controller for an engine/generator driven welder that reduces the output in response to potential stall conditions, and that does so at a magnitude responsive to the severity of the stall conditions and the arc condition is desirable.
According to a first aspect of the invention an engine/generator driven welding power supply includes an engine, and a generator driven by the engine. A welding power supply is connected to the generator output, and provides welding power. A controller controls the apparatus, and receives an RPM input signal indicative of the engine RPM, and a user selected magnitude input. The controller includes an output reduction circuit that reduces the magnitude of the welding power by a variable amount in the event the engine is likely to stall, so as to reduce the likelihood of a stall, but maintains sufficient power for a welding arc.
According to a second aspect of the invention an engine/generator driven welding power supply includes a user selectable magnitude input, an engine, a generator, a welding power supply and a controller. A feedback circuit provides RPM feedback to the controller. The controller includes an output reduction circuit that reduces the magnitude of the welding power by an amount responsive to the engine speed in the event that the engine RPM is less than an RPM threshold and the user selectable magnitude input is greater than a threshold.
According to a third aspect of the invention an engine/generator driven welding power supply includes a user selectable magnitude input, an engine, a generator, a welding power supply and a controller. The controller includes an output reduction circuit that reduces the magnitude of the welding power by an amount responsive to the user selectable setting in the event that the user selectable setting is greater than a threshold.
According to a fourth aspect of the invention a method of controlling an engine/generator driven welding power supply includes determining a user selected magnitude setting and providing a welding output responsive to the user selected magnitude setting. Also, the speed of the engine is determined and the magnitude of the welding output is reduced by a variable amount in the event the engine is likely to stall so as to reduce the likelihood of a stall, but maintain sufficient power for a welding arc.
According to a fifth aspect of the invention a method of controlling an engine/generator driven welding power supply includes determining a user selected magnitude setting and providing a welding output responsive to the user selected magnitude setting. Also, the speed of the engine is determined and the magnitude of the welding output is reduced by an amount responsive to the engine RPM in the event that the engine RPM is less than an RPM threshold, and that the user selected magnitude setting is greater than a threshold.
Accordingly to a sixth aspect of the invention a method of controlling an engine/generator driven welding power supply includes determining a user selected magnitude setting and providing a welding output responsive to the user selected magnitude setting. Also, the speed of the engine is determined and the magnitude of the welding output is reduced by an amount responsive to the user selected magnitude setting in the event that the engine user selected magnitude setting is greater than a threshold.
The output reduction circuit controls the generator field current to reduce the welding power in one embodiment, and it controls the load current command in another embodiment.
The output reduction circuit begins to act when the engine RPM is less than an RPM threshold in another embodiment, and the reduction is: dependent on the difference between the RPM threshold and the engine RPM, proportional to the difference between the RPM threshold and the engine RPM, or done in steps in various embodiments.
The output reduction circuit begins to act when the user selected magnitude setting is greater than a threshold, or responsive to the difference between the threshold and the user selected magnitude setting, or adjusted in steps in steps responsive to the difference between the threshold and the user selected magnitude setting, in various alternatives.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.